Receiver and event-detection-time-point estimation method

ABSTRACT

A data reception unit as the receiver is a device for estimating an event detection time point and includes: a reception-time-point measurement unit that measures a reception time point when reception is made by a reception I/F unit; a reception-time-point expected value calculation unit that calculates a reception-time-point expected value which is an expected value of a next reception time point when detection data is subsequently received, from the reception time point and a sampling period; a jitter amount estimation unit that calculates a variation amount of the reception time point with respect to the reception-time-point expected value, as a system delay jitter amount; and an event-detection-time-point estimation unit that estimates an event detection time point, from a system delay time measured in advance, the reception-time-point expected value and the system delay jitter amount.

TECHNICAL FIELD

The present invention relates to a receiver for receiving data and amethod of estimating an event detection time point.

BACKGROUND ART

If there is a long time interval (system delay time) from a time point(event detection time point) when a detector (sensor) provided on a roaddetects a situation (event) on the road to a time point (reception timepoint) when a receiver in a vehicle receives traffic guide information(detection data) based on the detection, there is the following problem:the received traffic guide information indicates old information (lowreliable information). As a countermeasure against this problem, PatentDocument 1 describes a device that acquires in advance an average valueof the system delay time (average system delay time) in an informationprovision system, subtracts the average system delay time from thereception time point when the vehicle receives the traffic guideinformation, and thus estimates (calculates) the event detection timepoint. With the device, it is possible to remove, from the receivedtraffic guide information, old information (low reliable information)detected at a time point (past time point) five minutes or more beforethe current time.

Patent Document 2 describes a vehicle-mounted device for identifying thesame vehicle, by using travel information produced as a consequence ofdetecting an event by a detector (sensor) installed in a vehicle andinformation received by a communication terminal in this vehicle (travelinformation transmitted from another vehicle). In the vehicle-mounteddevice, the sensor, the communication terminal, a controller, the GPS(Global Positioning System) and a control ECU (Electronic Control Unit)for controlling an engine and a brake are connected with each other,through a bus of a CAN (Controller Area Network) which is an in-carnetwork. Information indicating the result of the detection by thedetector installed in the vehicle (own vehicle) is produced at intervalsof 100 milliseconds. Information detected by the another vehicle istransmitted from a communication terminal (transmitter) in the anothervehicle at intervals of several hundred milliseconds. If a time pointindicated in time-point information added to the information received bythe vehicle (own vehicle) is a time point (past time point) a thresholdvalue or more before the current time, the received information is oldinformation (low reliable information) and accordingly the informationis removed.

PRIOR ART REFERENCE Patent Reference

-   Patent Document 1: Japanese Patent Application Publication No.    2012-194759-   Patent Document 2: Japanese Patent Publication No. 5702400

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, the device described in Patent Document 1 subtracts the averagesystem delay time (an average value of the system delay time caused bydata-generation-processing time and data transmission time) from thereception time point when the communication terminal (receiver) in thevehicle receives the traffic guide information, thereby estimating(calculating) the event detection time point which is a time point inthe transmitter (transmitter-side time point). If thedata-generation-processing time or the data transmission time greatlyvaries, the average system delay time greatly varies, and accordinglythere is the following problem: an error of the estimated eventdetection time point with respect to a time point (actual eventdetection time point) when the detector actually detects the eventgreatly varies, and information which has not been removed may containold information (low reliable information).

The device described in Patent Document 2 evaluates a time point whenthe information transmitted from the communication terminal(transmitter) in the another vehicle is received, but does not take thesystem delay time (delay time caused by the data-generation-processingtime and the data transmission time) into consideration. For thisreason, the process for estimating the event detection time point is notperformed, and there is the following problem: information which has notbeen removed may contain old information (low reliable information).

The present invention has been made for solving the problems of theconventional art, and an object of the present invention is to provide areceiver capable of accurately estimating an event detection time pointand an event detection-time-point estimation method used for accuratelyestimating the event detection time point.

Means for Solving the Problem

A receiver according to an aspect of the present invention is a receiverfor receiving detection data sent from a sensor that detects an event ineach fixed sampling period to estimate an event detection time pointwhich is a time point when the sensor detects the event. The receiverincludes: a reception unit to receive the detection data; areception-time-point measurement unit to measure a reception time pointwhich is a time point when the detection data is received by thereception unit; a reception-time-point expected value calculation unitto calculate a reception-time-point expected value which is an expectedvalue of a next reception time point which is a time point whendetection data is subsequently received, from the reception time pointand the sampling period; a jitter amount estimation unit to calculate avariation amount of the reception time point with respect to thereception-time-point expected value, as a system delay jitter amount;and an event-detection-time-point estimation unit to estimate the eventdetection time point, from a system delay time measured in advance as atime period from the time point when the sensor detects the event to thereception time point, the reception-time-point expected value and thesystem delay jitter amount.

An event-detection-time-point estimation method according to anotheraspect of the present invention is a method of estimating, in a receiverfor receiving detection data sent from a sensor that detects an event ineach fixed sampling period, an event detection time point which is atime point when the sensor detects the event. The method includes: astep of measuring a reception time point which is a time point when thedetection data is received by the receiver; a step of calculating areception-time-point expected value which is an expected value of a nextreception time point which is a time point when detection data issubsequently received, from the reception time point and the samplingperiod; a step of calculating a variation amount of the reception timepoint with respect to the reception-time-point expected value, as asystem delay jitter amount; and a step of estimating the event detectiontime point, from a system delay time measured in advance as a timeperiod from the time point when the sensor detects the event to thereception time point, the reception-time-point expected value and thesystem delay jitter amount.

Effects of the Invention

According to the present invention, it is possible to accuratelyestimate an event detection time point and therefore prevent occurrenceof a situation in which old information (low reliable information) isnot removed and a situation in which information which is not old isremoved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically showing a configuration of areceiver according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an outline of a method of estimating anevent detection time point by the receiver according to the firstembodiment.

FIG. 3 is a diagram showing an outline of a method of estimating anevent detection time point by a receiver in a comparison example.

FIG. 4 is a timing chart showing the method of estimating an eventdetection time point by the receiver according to the first embodiment.

FIG. 5 is a flowchart showing a process of calculating areception-time-point expected value by a reception-time-point expectedvalue calculation unit in the receiver according to the first embodimentand in a receiver according to a second embodiment.

FIG. 6 is a flowchart showing a process of estimating an event detectiontime point by an event-detection-time-point estimation unit in thereceiver according to the first embodiment.

FIG. 7 is a flowchart showing a process of estimating a system delayjitter amount by a jitter amount estimation unit in the receiveraccording to the first embodiment.

FIG. 8 is a flowchart showing a process of detecting an abnormal delayby an abnormal delay detection unit in the receiver according to thefirst embodiment and in the receiver according to the second embodiment.

FIG. 9 is a diagram showing an example of a system delay distributionused for simulations in FIG. 10 and FIG. 11.

FIG. 10 is a diagram showing an example of estimation errors of eventdetection time points obtained through a simulation in the firstembodiment.

FIG. 11 is a diagram showing an example of estimation errors of eventdetection time points obtained through a simulation in the comparisonexample.

FIG. 12 is a diagram showing a problem of the method of estimating anevent detection time point by the receiver according to the firstembodiment.

FIG. 13 is a block diagram schematically showing a configuration of thereceiver according to the second embodiment.

FIG. 14 is a diagram showing an outline of a method of estimating anevent detection time point by the receiver according to the secondembodiment.

FIG. 15 is a timing chart showing the method of estimating an eventdetection time point by the receiver according to the second embodiment.

FIG. 16 is a flowchart showing a process of estimating an eventdetection time point by the receiver according to the second embodiment.

FIG. 17 is a diagram showing an example of a system delay distributionused for a simulation in FIG. 18.

FIG. 18 is a diagram showing an example of estimation errors of eventdetection time points obtained through the simulations in the firstembodiment and the second embodiment.

FIG. 19 is a hardware configuration diagram showing a receiver of amodification example of the first embodiment and the second embodiment.

MODE FOR CARRYING OUT THE INVENTION (1) First Embodiment (1-1)Configuration in First Embodiment (Transmitter-Side Device and ReceptionSystem 10)

FIG. 1 is a block diagram schematically showing a configuration of areception system 10 according to a first embodiment of the presentinvention. As shown in FIG. 1, a plurality of sensors (also referred toas ‘sensor devices’) 170, 171, . . . , 172 for detecting events arecommunicably connected to a plurality of data reception units 100, 120,. . . , 140 as a plurality of receivers for receiving a plurality ofdetection data (sensor data) respectively, through a transmission path.

Each of the sensors 170, 171 and 172 is a transmitter-side component (atransmitter-side device) for transmitting detection data as a detectionresult which is a product of event detection. Detection targets of thesensors 170, 171 and 172 are not limited. For example, each of thesensors 170, 171 and 172 is a position sensor for detecting a positionof an object, a speed sensor for detecting a speed of an object, or thelike. Although the three sensors 170, 171 and 172 are shown in FIG. 1,the number of the sensors may be one, two, or four or more.

As shown in FIG. 1, the plurality of data reception units 100, 120 and140 and a synthesizing processing unit 161 form the reception system 10as a receiver-side system for receiving detection data. Although thethree data reception units 100, 120 and 140 are shown in FIG. 1, thenumber of the data reception units may be one, two, or four or more.

Each of the sensors 170, 171 and 172 performs sensing (event detection)in each fixed detection period (sampling period) Tsa, that is, atregular time intervals, processes a signal which is the product of thesensing, and sends, to a transmission path, a signal (detection data)which is the product of the processing. The transmission path is asignal transmission path for wireless communication or for wiredcommunication. The transmission path can be formed by using a networksuch as the Internet or a LAN (Local Area Network), a bus, a telephonecommunication network, a dedicated line or the like, for example. Thedetection data sent from the sensors 170, 171 and 172 at regularintervals are input to the data reception units 100, 120 and 140respectively, through the transmission path, for example. Each of thedata reception units 100, 120 and 140 estimates (calculates) a timepoint when the corresponding sensor of the sensors 170, 171 and 172installed in the transmitter-side device detects an event (eventdetection time point), makes the received detection data associated withthe estimated event detection time point TMS_i′, and then outputs theassociated data to the synthesizing processing unit 161. Receiving theassociated data from the data reception units 100, 120 and 140 (that is,receiving the plurality of data output from the plurality of datareception units), the synthesizing processing unit 161 performs aprocess of synthesizing the detection data on the basis of these data.

If the detection data sent from the sensors 170, 171 and 172 areposition data concerning an object as a detection target, for example,the synthesizing processing unit 161 makes the position data (detectiondata) indicating positions of the same object detected by the sensors170, 171 and 172 associated with estimation values TMS_i′ (i=0, 1, 2, .. . ) of time points (estimated event detection time points) when thesensors 170, 171 and 172 detect the object (detect the positions of theobject), thereby making it possible to grasp (calculate) the position ofthe object at a time point different from the event detection time pointTMS_i′. The synthesizing processing unit 161 may include a storage unit161 a for storing information (past data) containing the object positiondata (detection data) and the estimated event detection time pointsTMS_i′ that are associated with each other. The storage unit 161 a maybe a part of the synthesizing processing unit 161 or may be a storageunit provided outside the synthesizing processing unit 161. By treatingthe position of the object detected by each of the sensors 170, 171 and172 as a function of time, the synthesizing processing unit 161 cangrasp (calculate) the position of the object at an arbitrary time point.Thus, the reception system 10 shown in FIG. 1 can grasp (calculate) theobject position, such as a current position of the object as thedetection target or a future position (prediction position) of theobject as the detection target. Further, the synthesizing processingunit 161 can judge whether or not objects (detection targets) detectedby the sensors 170, 171 and 172 are the same object. Furthermore, thesynthesizing processing unit 161 makes efficient use of a plurality ofposition data included in a plurality of detection data sent from thesensors 170, 171 and 172, and therefore can improve the reliability ofthe detected object position data. In order to perform the synthesizingprocess with high accuracy, not only the object position data detectedby the sensors 170, 171 and 172 but also accurate time-point information(event detection time points) on time points when the object is detectedby the sensors 170, 171 and 172 are required. The following is adescription of how the reception system 10 according to the firstembodiment estimates the time point when the sensor detects the object,that is, the event detection time point TMS_i′, with high accuracy.

(Data Reception Units 100, 120 and 140)

The data reception units 100, 120 and 140 are basically the same inconfiguration as each other. So, the configuration of the data receptionunit 100 will be described below. The data reception unit 100 includes:a reception I/F (interface) unit 101 as a reception unit for receivingdetection data sent from a sensor (e.g., the sensor 170); and areception-time-point measurement unit 102 for measuring a time point(reception time point) when the detection data is received (i.e.,acquiring the reception time point), by referring to a system time pointfrom a system clock 160 every time when receiving from the reception I/Funit 101 a data reception notification of the reception of the detectiondata. The reception I/F unit 101 successively receives detection data. Areception time point when i-th (i is an integer not less than zero)received detection data is received is denoted as ‘Tr_i’. The systemclock 160 can be a clock for measuring a time point or a device forreceiving a signal indicating a time point provided from outside (a timesignal receiver), for example. FIG. 1 shows the system clock 160 as acomponent separate from the receivers, however, the system clock 160 maybe a part of the receiver or may be a part of the synthesizingprocessing unit 161.

The data reception unit 100 further includes a reception-time-pointexpected value calculation unit 103. The reception-time-point expectedvalue calculation unit 103 calculates an average system delay jitteramount that is a distribution mean value of variation time components(system delay jitter amount) Tj_i concerning system delay time that is atime period from a time point when the sensor for transmitting detectiondata detects an event (event detection time point) to a time point(reception time point) Tr_i when the reception I/F unit 101 receives thedetection data. The average system delay jitter amount concerning i-threceived detection data is denoted as ‘Tj_me_i’. The sampling periodthat is a fixed detection interval between detections of the event bythe sensor is denoted as ‘Tsa’. The calculation of the average systemdelay jitter amount Tj_me_i is expressed by the following equations (1)and (2), where N is a predetermined sample number (positive integer) andK is an integer increased by 1 at each time sampling is performed (K=0,1, 2, . . . ).

$\begin{matrix}{{{Tj}_{—}{me}_{—}i} = {\frac{1}{N}{\sum\limits_{i = {K - N}}^{K - 1}\; {{Tj}_{—}i}}}} & (1) \\{{{Tj}_{—}i} = {{{Tr}_{—}i} - \left( {\left( {{{Ta}_{—}{me}_{—}i} - 1} \right) + {Tsa}} \right)}} & (2)\end{matrix}$

However, when first detection data is received, as shown in steps S103and S104 in FIG. 5 described later, the above equation (1) is replacedwith Tj_me_i=Tr_0. When detection data is received until K reaches orexceeds the predetermined sample number N, equation (1) is replaced withthe following equation (1′), as shown in step S107 in FIG. 5 describedlater.

$\begin{matrix}{{{Tj}_{—}{me}_{—}i} = {\frac{1}{K}{\sum\limits_{i = 0}^{K - 1}\; {{Tj}_{—}i}}}} & \left( 1^{\prime} \right)\end{matrix}$

Next, the reception-time-point expected value calculation unit 103calculates a new reception-time-point expected value (an expected valueof a next reception time point when detection data is subsequentlyreceived) Ta_me_i, by adding the sampling period Tsa and the calculatedaverage system delay jitter amount Tj_me_i to a reception-time-pointexpected value (Ta_me_i−1) which is calculated when immediatelypreceding detection data is received. This calculation is performedaccording to the following equation (3).

Ta_me_i=(Ta_me_i−1)+Tsa+Tj_me_i  (3)

The data reception unit 100 further includes anevent-detection-time-point estimation unit 105 for estimating(calculating) an event detection time point TMS_i′, by subtracting, fromthe reception-time-point expected value Ta_me_i, an average system delaytime Tt_me calculated from measured values obtained by measuring thesystem delay time in advance. This calculation is performed according tothe following equation (4).

TMS_i′=Ta_me_i−Tt_me  (4)

FIG. 2 is a diagram showing an outline of a method of estimating theevent detection time point TMS_i′ by the data reception unit 100according to the first embodiment. The data reception unit 100 accordingto the first embodiment calculates the reception-time-point expectedvalue Ta_me_i from the detection data received by the data receptionunit 100 by using the above equations (1) to (3), subtracting theaverage system delay time Tt_me measured in advance from thereception-time-point expected value Ta_me_i as shown in the aboveequation (4), and thus estimates the event detection time point TMS_i′which is a time point when the sensor in the transmitter-side devicedetects the event. In this case, there is small fluctuation of error ofthe estimated event detection time point TMS_i′ with respect to theactual event detection time point TMS_i.

FIG. 3 is a diagram showing an outline of a method of estimating anevent detection time point TMS_ia by a receiver in a comparison example.In FIG. 3, ‘Tt_me’ represents an average value of the system delay timemeasured in advance (average system delay time) and ‘Tr_i’ represents areception time point when detection data is received. In the comparisonexample, if the average system delay time is constant, the eventdetection time point TMS_ia at the sensor is calculated according to thefollowing equation (5). In this case, there is greater fluctuation oferror of the estimated event detection time point TMS_ia with respect toan actual event detection time point TMS_i, than that in the case ofFIG. 2.

TMS_ia=Tr_i−Tt_me  (5)

(1-2) Operation in First Embodiment

FIG. 4 is a timing chart showing the method of estimating the eventdetection time point by the data reception unit 100 according to thefirst embodiment. In FIG. 4, a time point (actual event detection timepoint) when the sensor 170 detects the object (performs sensing) isdenoted as ‘TMS_i’ (i=0, 1, 2, . . . ). Detection data generated after alapse of internal delay time taken for internal processing in the sensor170 is denoted as ‘No. i’ (i=0, 1, 2, . . . ). The detection data sentfrom the transmitter-side device to the transmission path is received ata time point Tr_i (i=0, 1, 2, . . . ) by the data reception unit 100 inthe reception system 10, after a lapse of transmission delay time. Inthe data reception unit 100, the reception I/F unit 101 performs areception process. Specifically, in the data reception unit 100, datastored in a reception buffer in the reception I/F unit 101 is read outthrough a reception interruption process, the data is transferred to anassociation information addition unit 109, and then stored in theassociation information addition unit 109. In parallel with this, thereception I/F unit 101 sends, to the reception-time-point measurementunit 102, a data reception notification for notifying of the datareception. The event detection time point TMS_i′ estimated by theevent-detection-time-point estimation unit 105 is made to be associatedwith the detection data stored in the association information additionunit 109 and thus stored in the association information addition unit109.

The sensor detects an event at regular detection intervals (samplingperiod) of Tsa and successively sends detection data. If the averagesystem delay time Tt_me is constant, each reception interval betweenreceptions of the detection data by the data reception unit 100 is aninterval equal to the sampling period Tsa. However, most of internalprocessing in the transmitter-side device equipped with the sensor 170or internal processing in the data reception unit 100 is executed byusing software, hence time (delay time) taken for the internalprocessing varies (fluctuates). In a case that multiple transmitter-sidedevices are connected to the same transmission path (e.g., a case of aCAN bus or the like), if timing of transmission from a lower-prioritydevice of the transmitter-side devices coincides with timing oftransmission from a higher-priority device of the transmitter-sidedevices, transmission of detection data from the lower-prioritytransmitter-side device should be waited until transmission processingby the higher-priority transmitter-side device is completed. In such acase that multiple transmitter-side devices are connected to the sametransmission path, transmission delay time generally varies(fluctuates). Accordingly, actual intervals between reception timepoints Tr_0, Tr_1, Tr_2, . . . , Tr_i when the reception is performed bythe data reception unit 100 do not have the fixed value but havedifferent values, as shown in FIG. 4.

In FIG. 4, ‘Tt_me’ denotes an average value of the system delay timemeasured in advance (average system delay time). If the average systemdelay time Tt_me is constant, it is possible to accurately calculate theevent detection time point TMS_ia in the sensor 170 according to theabove equation (5) (the estimation method of the comparison example).However, since the actual average system delay time Tt_me fluctuates,the estimated event detection time point TMS_ia calculated according toequation (5) (the estimation method of the comparison example) greatlyfluctuates.

Thus, under circumstances where the average system delay time Tt_mevaries, the data reception unit 100 according to the first embodimentestimates the event detection time point TMS_i′ in the sensor 170 byusing the reception-time-point expected value. In the first embodiment,the reception I/F unit 101 receives detection data and then outputs adata reception notification to the reception-time-point measurement unit102. Every time when receiving the data reception notification, thereception-time-point measurement unit 102 acquires a current time pointfrom the system clock 160 and notifies the reception-time-point expectedvalue calculation unit 103 of the acquired current time point as thereception time point Tr_i.

Meanwhile, the system delay time is measured multiple times in advance,an average value (average system delay time) Tt_me of multiple values ofthe system delay time measured in advance is calculated, and the averagesystem delay time Tt_me is stored in an average-system-delay-timestorage unit 106.

(Sampling Period Storage Unit 104)

A sampling period storage unit 104 stores in advance the detectionperiod (sampling period) Tsa in which the sensor 170 detects an event(e.g., detects an object).

(Reception-Time-Point Expected Value Calculation Unit 103)

The reception-time-point expected value calculation unit 103 calculatesa reception-time-point expected value Ta_me_i according to the aboveequation (3), from an average value (average system delay jitter amount)Tj_me_i of a variation amount (system delay jitter amount) of an arrivaltime point Tj_i with respect to the fixed detection period (samplingperiod) Tsa, as shown in FIG. 4. The reception-time-point expected valueTa_me_i is calculated from N past reception time points and the samplingperiod Tsa. Specifically, the reception-time-point expected valueTa_me_i is obtained, by acquiring N system delay jitter amounts Tj_i asa deviation (system delay jitter amount) from the reception-time-pointexpected value when data is received, calculating the average systemdelay jitter amount Tj_me_i which is a moving average value of the Nsystem delay jitter amounts according to the above equation (1), andadding the average system delay jitter amount Tj_me_i to((Ta_me_i−1)+Tsa) as shown in the above equation (3). The eventdetection time point TMS_i′ estimated in the first embodiment iscalculated according to the above equation (4).

FIG. 5 is a flowchart showing a process of calculating thereception-time-point expected value Ta_me_i by the reception-time-pointexpected value calculation unit 103 in the data reception unit 100according to the first embodiment. First, in step S101, K (K=0, 1, 2, .. . ) is set to an initial value of 0, and then, in step S102, thereception-time-point expected value calculation unit 103 judges whetheror not it is the first reception of detection data after activation ofthe data reception unit 100. If it is the first reception (YES in stepS102), the process proceeds to step S103 and a process of setting thesystem delay jitter amount Tj_i=Tj_K to a value of 0 (initialization) isperformed. In other words, the reception-time-point expected valuecalculation unit 103 sets as Tj_i=0 on the assumption that the firstreceived detection data includes no system delay jitter amount, sets thereception-time-point expected value Ta_me_i as the first reception timeTr_0 in step S104, and then advances the process to step S110. In thenext step S110, the reception-time-point expected value calculation unit103 notifies the event-detection-time-point estimation unit 105 and ajitter amount estimation unit 107 of the reception-time-point expectedvalue Ta_me_i, increases N by 1, and then returns the process to stepS102.

If it is judged in step S102 that the reception is not the firstreception (NO in step S102), the reception-time-point expected valuecalculation unit 103 calculates the system delay jitter amount Tj_i instep S104 by using the above equation (2) and then advances the processto step S105. In this process, as shown in the above equation (2), amoving average of past system delay jitter amounts Tj_i is calculated.In the next step S106, the reception-time-point expected valuecalculation unit 103 judges whether or not N data necessary for apredetermined moving average process have been already received. If thenumber of detection data has not yet reached the necessary number ofdata (if K is smaller than the predetermined sample number N in stepS106), it is judged as NO and the process proceeds to step S107. In stepS107, the average system delay jitter amount Tj_me_i is calculatedaccording to the above equation (1′). Then, in step S109, thereception-time-point expected value Ta_me_i is calculated according tothe above equation (3). In the next step S110, the reception-time-pointexpected value calculation unit 103 notifies theevent-detection-time-point estimation unit 105 and the jitter amountestimation unit 107 of the reception-time-point expected value Ta_me_i,increases K by 1, and then returns the process to step S102.

If the number of detection data K reaches or exceeds the predeterminedsample number N, it is judged as YES in step S106, the process proceedsto step S109. In step S108, the average system delay jitter amountTj_me_i is calculated by using the above equation (1). In step S109, thereception-time-point expected value Ta_me_i is calculated according tothe above equation (3). Next, in step S110, the reception-time-pointexpected value calculation unit 103 notifies theevent-detection-time-point estimation unit 105 and the jitter amountestimation unit 107 of the reception-time-point expected value Ta_me_i,increases N by 1, and then returns the process to step S102.

As described above, each time when receiving new detection data from thereception-time-point measurement unit 102, the reception-time-pointexpected value calculation unit 103 is notified of a time point of thereception and performs the process shown in FIG. 5.

(Event-Detection-Time-Point Estimation Unit 105)

FIG. 6 is a flowchart showing a process of estimating the eventdetection time point TMS_i′ by the event-detection-time-point estimationunit 105 in the data reception unit 100 according to the firstembodiment. The reception-time-point expected value calculation unit 103notifies the event-detection-time-point estimation unit 105 of thereception-time-point expected value Ta_me_i, and then, in step S111, theevent-detection-time-point estimation unit 105 estimates (calculates)the event detection time point TMS_i′ by using the above equation (4).Then, in step S112, the event-detection-time-point estimation unit 105notifies the association information addition unit 109 of the estimatedevent detection time point TMS_i′ to make the association informationaddition unit 109 store the estimated event detection time point TMS_i′.

Receiving the estimated event detection time point TMS_i′, theassociation information addition unit 109 makes the estimated eventdetection time point TMS_i′ associated with the detection data from thesensor 170 which has been already supplied through the reception I/Funit 101 and temporarily stored in the association information additionunit 109, and then transmits the associated data to the synthesizingprocessing unit 161.

(Jitter Amount Estimation Unit 107)

FIG. 7 is a flowchart showing a process of estimating the system delayjitter amount Tj_i by the jitter amount estimation unit 107 in the datareception unit 100 according to the first embodiment. In step S121 inFIG. 7, the jitter amount estimation unit 107 judges whether or not itis the first reception of detection data after activation of the datareception unit 100. If it is the first reception, the system delayjitter amount Tj_i is initialized to zero in step S122. If it is not thefirst reception of the detection data in step S121, the jitter amountestimation unit 107 calculates the system delay jitter amount Tj_i instep S123 by using the above equation (2). Next, in step S124, thejitter amount estimation unit 107 notifies the association informationaddition unit 109 of the system delay jitter amount Tj_i.

(Abnormal Delay Detection Unit 108)

FIG. 8 is a flowchart showing a process of detecting an abnormal delayby an abnormal delay detection unit 108 in the data reception unit 100according to the first embodiment. By receiving the system delay jitteramount Tj_i from the jitter amount estimation unit 107 as an input, theabnormal delay detection unit 108 judges whether or not the estimatedsystem delay jitter amount Tj_i is an abnormal delay amount. In stepS131 in FIG. 8, the abnormal delay detection unit 108 judges whether ornot the system delay jitter amount Tj_i is a delay exceeding a presetpermissible amount (threshold value). If it is judged to be larger thanthe threshold value, the abnormal delay detection unit 108 notifies, instep S132, the association information addition unit 109 of abnormaldelay flag information indicating that the system delay is abnormal. Ifthe system delay jitter amount Tj_i is smaller than the threshold valuein step S131, the abnormal delay detection unit 108 notifies, in stepS133, the association information addition unit 109 of abnormal delayflag information indicating that the system delay is within a normalrange.

(Association Information Addition Unit 109)

Receiving the notification from the jitter amount estimation unit 107,the association information addition unit 109 makes the system delayjitter amount Tj_i associated with the detection data from the receptionI/F unit 101 and stores the associated system delay jitter amount Tj_i.Receiving the notification of the abnormal delay flag information fromthe abnormal delay detection unit 108, the association informationaddition unit 109 makes the abnormal delay flag information associatedwith the detection data from the reception I/F unit 101 and stores theassociated abnormal delay flag information.

Thus, the detection data from the reception I/F unit 101 is associatedwith the event detection time point TMS_i′, the system delay jitteramount Tj_i and the abnormal delay flag information, and thesynthesizing processing unit 161 is notified of the detection data fromthe reception I/F unit 101 together with information on all these itemsor information on at least one of these items.

(1-3) Advantageous Effect of First Embodiment

FIG. 9 is a diagram showing an example of a system delay distributionused for simulations in FIG. 10 and FIG. 11. FIG. 10 is a diagramshowing an example of estimation errors of event detection time pointsobtained through the simulation in the first embodiment. FIG. 11 is adiagram showing an example of estimation errors of event detection timepoints obtained through the simulation in the comparison example.

FIG. 9 shows the system delay distribution. In the simulations in FIG. 9to FIG. 11, the sampling period is 50 ms, the average system delay timeis 20 ms and system delays are produced at random so that the systemdelay jitter amount is within a range of ±10 ms. FIG. 10 shows theresult of the simulation of errors between estimated event detectiontime points TMS_i′ estimated by the data reception unit 100 according tothe first embodiment and actual event detection time points TMS_i, whensuch data is received by the data reception unit 100 according to thefirst embodiment.

FIG. 11 shows the result of the simulation of errors between eventdetection time points TMS_ia calculated in the comparison example, thatis, according to the above equation (4) and actual event detection timepoints TMS_i. The result indicates that, in the comparison example shownin FIG. 11, fluctuation in the system delay jitter amount within a rangeof ±10 ms directly influences the estimated event detection time points(TMS_ia in the above equation (5)), the influence of the fluctuationwithin a range of ±10 ms remains in the estimated event detection timepoints TMS_ia, and therefore time point estimation accuracy is poor.

In contrast, according to the configuration in the first embodiment,fluctuation of the system delay jitter amount within a range of ±10 msis removed from the estimated event detection time points TMS_i′, asshown in FIG. 10, and it is possible to calculate an event detectiontime point which is estimated with high accuracy, even undercircumstances where the system delay time contains jitter.

As shown in FIG. 10, according to the configuration in the firstembodiment, in the system for transmitting data from the transmitter tothe receiver, it is possible to estimate the event detection time pointTMS_i′ by the receiver with high accuracy, even under circumstanceswhere the system delay time contains jitter.

It is possible to apply the configuration in the first embodiment to asystem in which a plurality of various sensors (the sensors 170, 171 and172 and the like in FIG. 1) are included, such as a camera installed ina vehicle, a millimeter wave radar, LIDAR (Light Detection and Rangingor Laser Imaging Detection and Ranging) and SONAR, for example, each ofthe sensors performs sensing (detection) in each fixed sampling period,raw data obtained through the sensing or data converted to informationsuch as object position information, relative distance information andobject type information is transmitted through an in-car network such asa CAN or a LAN (Local Area Network), and an ECU acquires these data andcontrols steering, a brake, an accelerator of an automobile. Forexample, in a case that sensor data captured by each of the sensors isinformation on a position of an object, it is possible to estimate withhigh accuracy a time point when each of the sensors detects an event,that is, a time point (event detection time point) when each of thesensors senses the object from the received object position information,to make received sensing data associated with the estimated eventdetection time point, and therefore to grasp accurately positions attime points of the sensing by the sensors. When the detection targetobject or the automobile is moving, it is possible to calculate a speedor acceleration of the object from latest several samples of objectposition data with estimated time points composed of estimated eventdetection time points and object positions at the time points, and it ispossible to estimate the current position of the object from this andthe current time point, with high accuracy.

For example, if ‘X(t1)’ denotes an object position vector onthree-dimensional coordinates of an object detected by the sensor at anestimated event detection time point (estimated sensing time point) t1and ‘v(t)’ denotes an object speed at a time point t, it is possible tocalculate an object position coordinate vector X(t) at the current timepoint t according to the following equation (6) with high accuracy andit is possible to estimate the current position with high accuracy.

X(t)=∫_(t1) ^(t) v(t)d(t)+X(t1)  (6)

This means that a system equipped with the receiver (theevent-detection-time-point estimation method) according to the firstembodiment is capable of estimating with high accuracy that the objectposition X(t1) captured by the sensor was a phenomenon at the time pointt1. A case that vehicles travelling at a speed of 100 km/h pass by eachother on a road will be considered, for example. When a sensor detectsan object at intervals of 100 ms, the both vehicles approach each otherapproximately 2.8 m during a period of 100 ms. If the estimation methodof the first embodiment is not used, an object position error of 2.8 mat maximum is contained until the next sample.

If a future object position is predicted according to equation (6) whilethe object position error is contained, influence of the error increasesand the estimation error of the object position becomes greater, and thereliability of an obstacle avoidance route for the vehicles obtained byusing the estimated vehicle positions may be consequently lowered, forexample. According to the receiver (the event-detection-time-pointestimation method) of the first embodiment, it is possible to estimate atime point when an object is at a certain position with high accuracy.Therefore, it is possible to calculate the position of the object as afunction of time according to equation (6), to predict a future positionof the object with high accuracy, and to accurately calculate a routewhich allows a vehicle to avoid an obstacle, as a vehicle travel route,for example.

Further, in the first embodiment, an association is established betweena detected object position and a time point of the detection (eventdetection time point). Therefore, when a process of judging whetherobjects are the same object or different objects is performed bysynthesizing data from a plurality of sensors, it is possible toestimate that objects captured by different sensors are the same object,with high accuracy.

In the first embodiment, the receiver is capable of estimating an eventdetection time point with high accuracy, without adding time-pointinformation by the transmitter. Thus, a time-point addition function ofthe transmitter-side device is not necessary and a sensor can beselected more freely. For example, it is not usual for various sensorsinstalled in an automobile to include a sensor with a time additionfunction of adding a time point of sensing. In a case that it is usedfor use of controlling steering, a brake and an accelerator by an ECU,through an in-car network such as a CAN according to object positioninformation from these sensors, multiple sensors should be used.However, in such a system, it is difficult to use a sensor with thefunction of adding a time point of sensing. In the first embodiment, asensor without the function of adding time point information todetection data can be used as the sensor.

Moreover, in the first embodiment, even if the multiple sensors do nothave the function of adding a time point of sensing, the receiver iscapable of estimating a time point of sensing with high accuracy, andtherefore it is possible to reduce cost of the system using multiplesensors.

Furthermore, in the first embodiment, notification of the detection datais performed by making the detection data associated with the systemdelay jitter amount or notification of the detection data is performedby making the detection data associated with the abnormal delay flaginformation, and therefore it is possible to grasp, from the size of thedelay jitter amount, abnormal increase in load on the system or trafficjam conditions on the transmission path and it is possible to evaluatethe degree of stability of the system. Moreover, in the firstembodiment, if the system delay amount is a great delay amount thatexceeds a permissible level, it is judged that the reliability of thedetection data is low and the use of the detection data can beaccordingly prevented, and therefore it is possible to avoid abnormaloperation.

(2) Second Embodiment (2-1) Configuration in Second Embodiment

The performance of the data reception units 100, 120 and 140 as thereceivers according to the first embodiment may be influenced by achange in circumstances (for example, a function of limiting the numberof times of retrying data transmission). This is because there are somesystems provided with a function of limiting the number of times of datatransmission from a transmitter-side device to a transmission path inorder to prevent extreme increase in transmission load, and the functionmay cause the average system delay time Tt_me measured in advance togreatly vary. In contrast, in data reception units 200, 220 and 240 asreceivers according to the second embodiment, a shortest system delaytime Tt_min that is comparatively less influenced by a change incircumstances is used instead of the average system delay time Tt_me.Therefore, even in a case that the function of limiting the number oftimes of data transmission from a transmitter-side device to atransmission path works, it is possible to suppress variation in theperformance of the data reception units 200, 220 and 240.

FIG. 13 is a block diagram schematically showing a configuration of thedata reception units 200, 220, . . . , 240 as the receivers according tothe second embodiment of the present invention. In FIG. 13, componentsthat are the same as or correspond to the components shown in FIG. 1 areassigned the same reference characters as the reference characters inFIG. 1. As shown in FIG. 13, the plurality of sensors 170, 171, . . . ,172 for detecting an event are communicably connected to the pluralityof data reception units 200, 220 and 240 for receiving detection data(sensor data) through a transmission path.

As shown in FIG. 13, the plurality of data reception units 200, 220 and240 and the synthesizing processing unit 161 form a reception system 20as a receiver-side system for receiving detection data. Although FIG. 1shows the three data reception units 200, 220 and 240, the number of thedata reception units may be one, two, or four or more.

The data reception units 200, 220 and 240 are basically the same inconfiguration as each other. Accordingly, the configuration of the datareception unit 200 will be described below. The data reception unit 200includes: a reception I/F unit 201 as a reception unit for receivingdetection data sent from a sensor (e.g., the sensor 170); and areception-time-point measurement unit 202 for measuring a time point(reception time point) when detection data is received (that is, foracquiring the reception time point) by referring to a system time pointfrom the system clock 160, every time when receiving from the receptionI/F unit 201 a data reception notification for notifying of reception ofdetection data. The reception I/F unit 201 successively receivesdetection data, and a reception time point when i-th (i is an integernot less than zero) received detection data is received is denoted as‘Tr_i’.

In the first embodiment, as shown in the above equation (4), the eventdetection time point TMS_i′ is calculated by subtracting the averagesystem delay time Tt_me measured in advance from thereception-time-point expected value Ta_me_i. Here, if a CAN which is anin-car network is used as a transmission path for communicablyconnecting the sensor and the data reception unit, for example, there isa protocol which fixes an upper limit to the number of times ofretrying, as a protocol for the CAN. If the number of times of retryingdata transmission reaches the fixed upper limit number (e.g., 256) dueto a trouble caused in the sensor connected to the CAN, this protocollimits data transmission from this transmitter-side device to the CAN,in order to prevent increase in transmission load caused by multipletimes of retrying. When such a situation occurs, a data transfer amounton the CAN decreases, the frequency of bus contention betweentransmitter-side devices at the time of data transmission accordinglydecreases, and thus the average system delay time Tt_me measured inadvance is shortened. In other words, as shown in FIG. 12, thereception-time-point expected value Ta_me_i in the data reception unitshifts (shifts in the leftward direction), due to a change incircumstances, from a reception-time-point distribution curve (a whiteline) before the change in circumstances to a reception-time-pointdistribution curve (a black line) after the change in circumstances.Consequently, in the data reception unit according to the firstembodiment, since the changed average system delay time Tt_me issubtracted from the leftward-shifted reception-time-point expected valueTa_me_i, the estimated event detection time point TMS_i′ estimated inthe first embodiment may greatly deviate from the actual event detectiontime point TMS_i.

To cope with this, each of the data reception units 200, 220 and 240according to the second embodiment includes a shortest-system-delay-timestorage unit 206 instead of the average-system-delay-time storage unit106, and additionally includes a jitter amount storage unit 210 (ajitter amount estimation unit 207 and the jitter amount storage unit 210constitute a shortest-system-delay-case jitter amount estimation unit207 a), as shown in FIG. 13. In these regards, the data reception units200, 220 and 240 according to the second embodiment differ from the datareception units 100, 120 and 140 according to the first embodiment. Thereception I/F unit 201, a reception-time-point measurement unit 202, areception-time-point expected value calculation unit 203, a samplingperiod storage unit 204, an abnormal delay detection unit 208 and anassociation information addition unit 209 in the second embodiment arethe same in function as the reception I/F unit 101, thereception-time-point measurement unit 102, the reception-time-pointexpected value calculation unit 103, the sampling period storage unit104, the abnormal delay detection unit 108 and the associationinformation addition unit 109 in the first embodiment respectively.Accordingly, equations (1), (1′), (2) and (3) in the first embodimentcan be also applied in the second embodiment.

In the second embodiment, a time point when the sensor in thetransmitter-side device detects an event is estimated in the followingmanner. The reception unit 200 according to the second embodiment usesthe following theory: the shortest system delay time Tt_min measured inadvance is equivalent to a shortest system delay time during operationafter the measurement in advance (that is, it can be regarded that bothare substantially equivalent), and the shortest system delay time Tt_mindoes not change even if the average system delay time Ta_me_i changesdue to a change in circumstances occurred during operation after themeasurement in advance. A bandwidth usage amount under normalcircumstances on a network as a transmission path is designed so as tobe a sufficiently small amount in comparison with a maximumcommunication amount available on the network. Accordingly, the shortesttime of the system delay time at the time of the measurement in advanceand the shortest time of the system delay time after the measurement inadvance are both shortest time periods in a case that data issuccessfully transmitted through the transmission path while no buscontention occurs, and these are considered to be the same time period(shortest system delay time) Tt_min. By defining a time obtained bysubtracting, from the reception-time-point expected value Ta_me_i, areception time point Tr_i when reception is made with the shortestsystem delay time, as a jitter amount (shortest-system-delay-case jitteramount) Tj_min when reception is made with the system delay time that isthe shortest (when reception is made in the shortest time), theshortest-system-delay-case jitter amount Tj_min can be calculated in thefollowing manner by the data reception unit 200 during operation. Thatis, in a case that detection data is received while the system delaytime is shortest, since the jitter amount Tj_i calculated by the jitteramount estimation unit 207 is maximum, if the reception time point Tr_iis earlier than the reception-time-point expected value Ta_me_i and ifthe jitter amount Tj_i calculated by the jitter amount estimation unit207 is greater than the past maximum value (if the jitter amount Tj_i isa new maximum value), the jitter amount Tj_i is stored in the jitteramount storage unit 210 as the shortest-system-delay-case jitter amountTj_min. By using these values, an event detection time point TMS_ib′ canbe calculated by subtracting, from the reception-time-point expectedvalue Ta_me_i, the shortest-system-delay-case jitter amount Tj_min andthe shortest system delay time Tt_min measured in advance, as shown inFIG. 14. This calculation can be expressed by the following equation(7).

TMS_ib′=Ta_me_i−Tj_min−Tt_min  (7)

(2-2) Operation in Second Embodiment

FIG. 15 is a timing chart showing a method of estimating the eventdetection time point TMS_ib′ in the data reception unit 200 according tothe second embodiment. In FIG. 15, parts that are the same as the partsshown in FIG. 4 are assigned the same reference signs. In FIG. 15, atime point when the sensor 170 detects an event (e.g., a position of anobject) is denoted as ‘TMS_i’ (i=0, 1, 2, . . . ) and data produced atthe time is denoted as ‘No. i’. Then, after a lapse of internal delaytime caused by internal processing in the sensor, the data is sent tothe transmission path. After a lapse of transmission delay time, thedetection data sent to the transmission path is received by the datareception unit 200 at a time point Tr_i (i=0, 1, 2, . . . ). In the datareception unit 200, the reception I/F unit 201 performs a receptionprocess. Specifically, the reception I/F unit 201 reads out data storedin a reception buffer in the reception I/F unit 201 through a receptioninterruption process, and transfers the data to the associationinformation addition unit 209. The reception I/F unit 201 concurrentlysends a data reception notification to the reception-time-pointmeasurement unit 202 to make an estimated event detection time pointTMS_ib′ that is estimated by an event-detection-time-point estimationunit 205 described later associated with the detection data in theassociation information addition unit 209 and to store the associateddata.

The sensor 170 detects the event in every fixed sampling period Tsa andsends data as the result of the detection to the transmission path. Ifthe system delay time is constant, timing of reception by the datareception unit 200 coincides with the fixed period Tsa, however,actually intervals between reception time points Tr_0, Tr_1, Tr_2, . . ., Tr_i when the data reception unit receives data do not have the fixedvalue Tsa but have different values as shown in FIG. 15.

In FIG. 15, ‘Tt_min’ denotes the value of the shortest time of thesystem delay (shortest system delay time) measured in advance. Receivingthe detection data, the reception I/F unit 201 notifies thereception-time-point measurement unit 202 of a data receptionnotification. Every time when receiving the data reception notification,the reception-time-point measurement unit 202 acquires a current timepoint (reception time point) Tr_i from the system clock 160 and notifiesthe reception-time-point expected value calculation unit 203 of thecurrent time point. Meanwhile, the shortest time of the system delay ismeasured in advance and the measured value is stored in the shortestsystem delay time storage unit 206. The sampling period storage unit 204stores the event detection period that is an interval between objectdetections by the sensor 170, that is, the sampling period that is aninterval between data outputs to the transmission path. Thereception-time-point expected value calculation unit 203 calculates thereception-time-point expected value Ta_me_i from an average value(average system delay jitter amount) Tj_me_i of the arrival-time-pointvariation amount (system delay jitter amount) Tj_i with respect to thereception timing of regular intervals, in FIG. 15.

The reception-time-point expected value Ta_me_i is calculated by usingthe above equation (3), in the same way as in the first embodiment. Thesystem delay jitter amount Tj_i calculated by using the above equation(2) is the amount of deviation from the reception-time-point expectedvalue (Ta_me_i−1)+Tsa. ‘Tj_min’ denotes a system delay jitter amountwhen reception is made in the shortest time (shortest-system-delay-casejitter amount), that is, a maximum jitter amount in a direction that thereception time point becomes earlier than the reception-time-pointexpected value Ta_me_i. The jitter amount storage unit 210 monitors thejitter amount at the time of data reception estimated by the jitteramount estimation unit 207 and stores the maximum jitter amount in thedirection that the reception time point becomes earlier. By using theabove definition, the event-detection-time-point estimation unit 205calculates the event detection time point TMS_ib′ in the sensor 170according to the above equation (7).

Specific operation by the reception unit 200 according to the secondembodiment for estimating the event detection time point TMS_ib′ in thesensor 170 described above will be described below. First, thereception-time-point expected value Ta_me_i is calculated by thereception-time-point expected value calculation unit 203. This processis the same as the process shown in the flowchart of FIG. 5 in the firstembodiment.

FIG. 16 is a flowchart showing a process of estimating the eventdetection time point TMS_ib′ in the data reception unit 200 according tothe second embodiment. The reception-time-point expected valuecalculation unit 203 notifies the event-detection-time-point estimationunit 205 of the reception-time-point expected value Ta_me_i, and thenthe event-detection-time-point estimation unit 205 performs a process ofcalculating the event detection time point TMS_ib′ by using equation (7)in step S211. Then, in step S212, the event-detection-time-pointestimation unit 205 notifies the association information addition unit209 of the calculated event detection time point TMS_ib′.

Receiving the event detection time point TMS_ib′ from theevent-detection-time-point estimation unit 205, the associationinformation addition unit 209 makes the event detection time pointTMS_ib′ associated with the detection data from the sensor 170 that hasbeen already temporarily stored through the reception I/F unit 201, andthe associated data is sent to the synthesizing processing unit 161.

(2-3) Advantageous Effect in Second Embodiment

FIG. 17 is a diagram showing an example of a system delay distributionused for a simulation shown in FIG. 18. FIG. 18 is a diagram showing anexample of estimation errors of event detection time points obtainedthrough simulations of the first and second embodiments. FIG. 17 shows acase that the sampling period is set to 50 ms and the average value ofthe system delay time changes from 20 ms to 30 ms during the operation(time point 25000 ms). Accordingly, in the example of FIG. 17, thesystem delay is produced so that the jitter amount of the system delaytime changes from ±10 ms to ±20 ms during the operation (time point25000 ms). FIG. 18 shows a result of a simulation of errors of the eventdetection time points TMS_ib′ estimated when the data reception unit 200according to the second embodiment receives such data and errors of theevent detection time points TMS_i′ estimated when the data receptionunit 100 in the first embodiment receives such data. As shown in FIG.18, when the average value of the system delay time changes from 20 msto 30 ms (at the time point 25000 ms), it is understood that the errorsof the event detection time points in the first embodiment steadilyoccur within a range of approximately 0 ms from 10 ms. On the otherhand, the errors of the event detection time points TMS_ib′ in thesecond embodiment are not affected by the change in the system delaytime, and it is understood that the estimation of time points can beperformed with robustness to changes in circumstances.

As described above, the data reception unit (theevent-detection-time-point estimation method) according to the secondembodiment is capable of estimating the event detection time pointTMS_ib′ with high accuracy in the system in which the transmittertransmits data to the data reception unit, even if the system delay timecontains jitter.

The data reception unit (the estimation method) according to the secondembodiment eliminates the need to provide the sensor with the functionof adding time information, and therefore improves system configurationflexibility.

Further, according to the second embodiment, in addition to theadvantageous effect shown in the first embodiment, it is possible forthe data reception unit 200 to estimate the event detection time pointTMS_ib′ with high accuracy in the system in which the transmittertransmits data to the data reception unit, even if the average systemdelay time changes. For example, if there is a device which stopstransmission operation among the sensors connected to the transmissionpath, the average system delay time decreases. As another example, in acase that a sensor connected to the transmission path starts operatingwhen it satisfies a certain condition (e.g., in a case that an infraredcamera starts operating when the brightness in the surroundingsdecreases such as in the night and video data obtained through sensingby the camera is transmitted to a network at regular intervals), thefrequency of occurrence of contention between the transmitter-sidedevices increases. In this case, since transmission of detection datafrom a lower-priority transmitter-side device is waited, the averagesystem delay time on the transmission path increases, with respect tothe detection data from the transmitter-side device. Even in such acase, by using the data reception unit according to the secondembodiment, it is possible to estimate a time point when the sensordetects an event with high accuracy.

Vehicle detection information contained in traffic guide informationdistributed to a vehicle is so considerably old information that trafficcondition far apart from the current condition is displayed as a displayof traffic information, such as traffic-jam information. This problemcan be solved by applying the data reception unit according to thesecond embodiment. Specifically, in a case that each of the sensors 170,171 and 172 performs vehicle detection at regular intervals of Tsa anddetected data is supplied to a traffic-guide-information productionsystem as the reception system through a network as the transmissionpath, the shortest time taken for the transmission to the reception I/Funit 201 included in the data reception unit is measured in advance andthe measured time is stored in the shortest-system-delay-time storageunit 206. The reception-time-point measurement unit 202 measures areception time point Tr_i when the reception I/F unit 201 receivesvehicle detection information. The reception-time-point expected valuecalculation unit 203 calculates a reception-time-point expected valueTa_me_i, through the processes shown in the flowchart of FIG. 5 based onequations (1), (2) and (3) from time points of past receptions and thevalue of the sampling period Tsa stored in the sampling period storageunit 204. The jitter amount storage unit 210 stores the maximum jitteramount that makes the reception time point earlier, of system delayjitter amounts Tj_i when data are received generated by the jitteramount estimation unit 207, as a jitter amount when the reception ismade in the shortest time (shortest-system-delay-case jitter amount). Byperforming the process, shown in equation (7), of subtracting theshortest-system-delay-case jitter amount Tj_min and the shortest systemdelay time Tt_me measured in advance from the reception-time-pointexpected value Ta_me_i, that is, according to the flowchart of FIG. 16,it is possible for the event-detection-time-point estimation unit 205 toestimate an event detection time point (vehicle detection time point)accurately, to make the estimated vehicle detection time point with thevehicle detection information received by the association informationaddition unit 209, and to output the associated information to aprocessing unit in a following stage.

Furthermore, even if there are fluctuations as shown in FIG. 9 in thesystem delay time that is a time period after vehicle detection by thesensor until reception by the traffic-guide-information productionsystem as the reception system, the data reception unit 200 according tothe second embodiment makes it possible to reduce an error of anestimated event detection time point to be extremely small as shown inFIG. 10.

Moreover, even if the average value of the system delay time changes asin FIG. 17, the data reception unit 200 according to the secondembodiment makes it possible to estimate with high accuracy withoutbeing affected by estimation of the event detection time point, asindicated by the result obtained through the method according to thesecond embodiment shown in FIG. 18.

As described above, according to the second embodiment, even if there isa change in the transmission delay time contained in the system delaytime, it is possible to estimate an event detection time pointaccurately. Accordingly, it is possible to produce traffic guideinformation without including event detection information on the pastbefore a certain threshold value.

Recently, various IOT (Internet of Things) services using varioussensors connected to a network as a transmission path and using big dataobtained through sensing by the sensors have been proposed, such asremote control operation of an object or the like at a distant location,an autonomous driving or driver-assistance system, detection of abnormalconditions of equipment or structure, prediction of abnormal conditions,generation and distribution of real-time traffic information by usingdata from sensors in vehicles or on roads, and watching or remotemonitoring services for the elderly. Each of such services uses a systemin which data are obtained through detection at regular intervals bysensors placed at distant locations and the obtained data aretransmitted through a network. By applying the data reception unitaccording to the second embodiment to the system, it is possible toestimate a time point of sensing accurately, even in a case that randomtransmission-path delay jitter is undesirably contained on atransmission path and the transmission delay time changes to variousvalues or the average transmission delay time changes. Therefore, it canbe applied to various uses.

(3) Modification Example

FIG. 19 is a hardware configuration diagram showing a configuration of amodification example of the data reception units according to the firstand second embodiments. The data reception units 100, 120 and 140 shownin FIG. 1 can be achieved by using a memory 91 as storage for storing aprogram as software and a processor 92 as an information processing unitfor executing the program stored in the memory 91 (for example, by usinga computer). In this case, the components 104, 106 and 109 in FIG. 1correspond to the memory 91 in FIG. 19, and the components 101, 102,103, 105, 107, 108 and 161 in FIG. 1 correspond to the processor 92executing the program. Some of the components 101, 102, 103, 105, 107,108 and 161 shown in FIG. 1 may be achieved by the memory 91 and theprocessor 92 executing the program that are shown in FIG. 19.

The data reception units 200, 220 and 240 shown in FIG. 13 can beachieved by using the memory 91 as storage for storing a program assoftware and the processor 92 as an information processing unit forexecuting the program stored in the memory 91 (for example, by using acomputer). In this case, the components 204, 206, 209 and 210 in FIG. 13correspond to the memory 91 in FIG. 19, and the components 201, 202,203, 205, 207, 208 and 161 in FIG. 13 correspond to the processor 92executing the program. Some of the components 201, 202, 203, 205, 207,208 and 161 shown in FIG. 13 may be achieved by the memory 91 and theprocessor 92 for executing the program that are shown in FIG. 19.

DESCRIPTION OF REFERENCE CHARACTERS

10, 20 reception system; 100, 120, 140 data reception unit (receiver);101 reception I/F unit (reception unit); 102 reception-time-pointmeasurement unit; 103 reception-time-point expected value calculationunit; 104 sampling period storage unit; 105 event-detection-time-pointestimation unit; 106 average-system-delay-time storage unit; 107 jitteramount estimation unit; 108 abnormal delay detection unit; 109association information addition unit; 160 system clock; 161synthesizing processing unit; 170, 171, 172 sensor; 200, 220, 240 datareception unit (receiver); 201 reception I/F unit (reception unit); 202reception-time-point measurement unit; 203 reception-time-point expectedvalue calculation unit; 204 sampling period storage unit; 205event-detection-time-point estimation unit; 206average-system-delay-time storage unit; 207 jitter amount estimationunit; 207 a shortest jitter amount estimation unit; 208 abnormal delaydetection unit; 209 association information addition unit; 210 jitteramount storage unit; Tsa sampling period (detection period); Tr_ireception time; Tt_me average system delay time; Ta_me_ireception-time-point expected value; Tj_i system delay jitter amount;TMS_i′, TMS_ib′ estimated event detection time point; Tj_me_i averagesystem delay jitter amount; Tj_min shortest-system-delay-case jitteramount; Tt_min shortest system delay time.

1. A receiver for receiving detection data sent from a sensor thatdetects an event in each fixed sampling period to estimate an eventdetection time point which is a time point when the sensor detects theevent, the receiver comprising: a reception unit to receive thedetection data; a reception-time-point measurement unit to measure areception time point which is a time point when the detection data isreceived by the reception unit; a reception-time-point expected valuecalculation unit to calculate a reception-time-point expected valuewhich is an expected value of a next reception time point which is atime point when detection data is subsequently received, from thereception time point and the sampling period; a jitter amount estimationunit to calculate a variation amount of the reception time point withrespect to the reception-time-point expected value, as a system delayjitter amount; and an event-detection-time-point estimation unit toestimate the event detection time point, from a system delay timemeasured in advance as a time period from the time point when the sensordetects the event to the reception time point, the reception-time-pointexpected value and the system delay jitter amount.
 2. The receiveraccording to claim 1, wherein the event-detection-time-point estimationunit calculates the event detection time point, by subtracting, from thereception-time-point expected value, an average system delay time whichis an average value of the system delay time.
 3. The receiver accordingto claim 1, wherein the reception-time-point expected value calculationunit calculates an average system delay jitter amount which is adistribution mean value of variation time components of the system delaytime, and obtains the reception-time-point expected value by adding thesampling period and the average system delay jitter amount to animmediately preceding reception-time-point expected value calculated ata time of reception of immediately preceding detection data.
 4. Thereceiver according to claim 1 further comprising an associationinformation addition unit to make the event detection time pointassociated with the detection data.
 5. The receiver according to claim4, wherein the jitter amount estimation unit estimates the system delayjitter amount, from the reception time point and thereception-time-point expected value, and the association informationaddition unit makes the system delay jitter amount associated with thedetection data.
 6. The receiver according to claim 4 further comprisingan abnormal delay detection unit to detect that a system delay isabnormal when the system delay jitter amount exceeds a prescribedthreshold value, wherein the association information addition unit makesinformation indicating that the system delay is abnormal associated withthe detection data.
 7. An event-detection-time-point estimation methodof estimating, in a receiver for receiving detection data sent from asensor that detects an event in each fixed sampling period, an eventdetection time point which is a time point when the sensor detects theevent, the method comprising: a step of measuring a reception time pointwhich is a time point when the detection data is received by thereceiver; a step of calculating a reception-time-point expected valuewhich is an expected value of a next reception time point which is atime point when detection data is subsequently received, from thereception time point and the sampling period; a step of calculating avariation amount of the reception time point with respect to thereception-time-point expected value, as a system delay jitter amount;and a step of estimating the event detection time point, from a systemdelay time measured in advance as a time period from the time point whenthe sensor detects the event to the reception time point, thereception-time-point expected value and the system delay jitter amount.8. The event-detection-time-point estimation method according to claim7, wherein the event detection time point is calculated by subtracting,from the reception-time-point expected value, an average system delaytime which is an average value of the system delay time.
 9. Theevent-detection-time-point estimation method according to claim 7,wherein the step of calculating the reception-time-point expected valueincludes: a step of calculating an average system delay jitter amountwhich is a distribution mean value of variation time components of thesystem delay time; and a step of obtaining the reception-time-pointexpected value, by adding the sampling period and the average systemdelay jitter amount to an immediately preceding reception-time-pointexpected value calculated at a time of reception of immediatelypreceding detection data.
 10. A receiver for receiving detection datasent from a sensor that detects an event in each fixed sampling periodto estimate an event detection time point which is a time point when thesensor detects the event, the receiver comprising: a reception unit toreceive the detection data; a reception-time-point measurement unit tomeasure a reception time point which is a time point when the detectiondata is received by the reception unit; a reception-time-point expectedvalue calculation unit to calculate a reception-time-point expectedvalue which is an expected value of a next reception time point which isa time point when detection data is subsequently received, from thereception time point and the sampling period; ashortest-system-delay-case jitter amount estimation unit to calculate amaximum value of a variation amount of the reception time point withrespect to the reception-time-point expected value, as ashortest-system-delay-case jitter amount; and anevent-detection-time-point estimation unit to estimate the eventdetection time point, from a shortest system delay time obtained bymeasuring in advance a shortest time period from the time point when thesensor detects the event to the reception time point, thereception-time-point expected value and the shortest-system-delay-casejitter amount.
 11. An event-detection-time-point estimation method ofestimating, in a receiver for receiving detection data sent from asensor that detects an event in each fixed sampling period, an eventdetection time point which is a time point when the sensor detects theevent, the method comprising: a step of measuring a reception time pointwhich is a time point when the detection data is received by thereceiver; a step of calculating a reception-time-point expected valuewhich is an expected value of a next reception time point which is atime point when detection data is subsequently received, from thereception time point and the sampling period; a step of calculating amaximum value of a variation amount of the reception time point withrespect to the reception-time-point expected value, as ashortest-system-delay-case jitter amount; and a step of estimating theevent detection time point, from a shortest system delay time obtainedby measuring in advance a shortest time period from the time point whenthe sensor detects the event to the reception time point, thereception-time-point expected value and the shortest-system-delay-casejitter amount.